Collagen is a fibrous protein which is found in all multicellular organisms, and occupies 25% of total proteins as a main component of a skin or a bone in mammals. A typical collagen molecule has a rope-like hyperhelical structure, in which three collagen polypeptide chains form a triple helix structure. Particularly, proline (Pro) and glycine (Gly) are contained in collagen at a large amount, and both amino acid residues are important for formation of a stable triple helix structure.
Examples of a method for using collagen as a biomaterial include a method for transplanting a pig skin tissue itself or a freeze-dried product thereof to a damaged part of the skin such as by burns, a method for using collagen after removing cellular components such as by enzyme treatment, and a method for using collagen obtained by solubilizing collagen by treatment with an acidic solution or an enzyme, and reconstituting this into a desired shape. Non-Patent Document 1 describes a general method of preparation of, and a general method of qualitative analysis of collagen.
There are various proposals about use of collagen.
For example, Patent Document 1 proposes a process for producing a collagen derivative which gives moisture to the skin and smoothes the skin, comprising modifying collagen by esterification of an animal tissue containing collagen with an alcohol, and extracting modified collagen, as well as a cosmetic base using it.
In addition, Patent Document 2 describes a process for producing water-soluble crosslinked collagen which has a high rate of reconstruction to a triple helix structure after heat denaturation, comprising a crosslinking-treating soluble collagen with an alkylene diimidate divalent cross-linker having an imide ester group at both terminals of a methylene chain.
In addition, Patent Document 3 describes a collagen-synthetic polymer matrix which is useful for preparation of a biocompatible implant which is low immunogenic and is used in various medical applications, prepared by reacting collagen with a first synthetic hydrophilic polymer to produce the collagen-synthetic polymer matrix, and reacting the collagen-synthetic polymer matrix with a second synthetic hydrophilic polymer, a biologically-active substance, glycosaminoglycan and a derivative thereof, a chemical cross-linker, an esterifying agent, an amidating agent, an acylating agent, an amino acid, and a polypeptide, etc.
In addition, Patent Document 4 describes a combined product comprising a hydrophilic synthetic polymer covalently-bonded with chemically modified collagen which is substantially in a non-fibrous form at pH 7. The document describes that the combined product is particularly useful in an ophthalmic device and that it is optically transparent and has biocompatibility.
In addition, Patent Document 5 describes a process for producing a membranous collagen substance, comprising grinding and cutting a collagen matrix, centrifuging the ground and cut matrix under a high centrifugal field, homogenizing a precipitate to prepare a paste, casting the paste, and drying the cast paste at 37° C. or lower. The document also describes that the membranous collagen substance is biocompatible and non-inflammatory, and useful for tissue restoration as an artificial implant.
In addition, Patent Document 6 describes highly purified soluble fish scale collagen, and a process for producing the collagen by pepsinating a fish scale itself or after deashing.
In addition, Patent Document 7 describes a process for producing dried granular or powdery soluble collagen, comprising ejecting a collagen solution into a 70-90% ethanol medium through a nozzle to produce a filamentous or membranous product, and drying, and cutting or grinding the product.
In addition, Patent Document 8 describes use of an un-calcined hydroxy-apatite single crystal as a material for restoration of a biological hard tissue such as a bone by attaching the un-calcined hydroxy-apatite single crystal to at least a part of a low antigenic collagen fibril.
In addition, Patent Document 9 describes a method for removing a prion in collagen which is derived from animals or humans, comprising removing a cell and tissue fragment in a collagen solution, and alkalinizing the collagen solution, as well as collagen prepared by this method.
In addition, Non-Patent Document 2 reports that, as to a method of chemical synthesis of a collagen analogue, soluble polyamide having a molecular weight of 16,000-21,000 is obtained by dissolving a p-nitrophenyl ester of Pro-Ser-Gly or a p-nitrophenyl ester of Pro-Ala-Gly in dimethylformamide (DMF), adding thereto triethylamine to allow to stand for 24 hours. Such soluble polyamide is deduced to form a triple-helix structure in the light of circular dichroism spectroscopy, but there is no description about a property of the resulting polymer.
In addition, Non-Patent Document 3 reports a method for preparing polyamide, comprising dissolving in dimethyl sulfoxide a 50-mer peptide containing the Val-Pro-Gly-Val-Gly (SEQ ID NO: 4) sequence derived from elastin, adding 2 equivalents of 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide, 1 equivalent of 1-hydroxybenzotriazole and 1.6 equivalents of N-methylmorpholine to the solution to allow to stand for 14 days, and dialyzing the solution with a 50,000 molecular weight-cut off dialysis membrane.
In addition, Patent Document 10 discloses that a polypeptide consisting of peptide units represented by the following formulas (1)-(3) can form a collagen tissue.[—(OC—(CH2)m—CO)p-(Pro-Y-Gly)n-]a  (1)[—(OC—(CH2)m—CO)q—(Z)r—]b  (2)[—HN—R—NH—]c  (3)(wherein m represents an integer of 1-18, p and q are the same or different and represent 0 or 1, Y represents Pro or Hyp, n represents an integer of 1-20, Z represents a peptide chain consisting of 1-10 amino acid residues, r represents an integer of 1-20, R represents a linear or branched alkylene group, a ratio between a and b is a/b=100/0-30/70 (molar ratio), and when p=1 and q=0, then c=a, when p=0 and q=1, then c=b, when p=1 and q=1, then c=a+b, and when p=0 and q=0, then c=0).
On the other hand, as described in aforementioned Patent Document 9, it has been said that a causative substance of a sheep tremor disease and bovine spongiform encephalopathy is an infectious protein called a prion, and this infectious protein is one cause of human Creutzfeldt-Jakob disease infection. Non-Patent Document 4 points out that the prion is a protein that is hardly inactivated by a usual sterilization or disinfection method and is infectious across species.
Generally, a medical device, a medicine or a cosmetic often uses collagen derived from cattle or pigs as a raw material. Thus, there is a continued risk of infection (or propagation) with a pathogen (or a pathogenic factor) such as the prion that cannot be removed by the usual sterilization or disinfection method.
In addition, since natural collagen contains various cell adhesive sites, it cannot exert cell selectivity depending upon its application. For example, when collagen is used as a nerve axon-guiding material, an axon cannot extend since a migration rate and a growth rate of a surrounding fibroblast is larger than an extending rate of an axon and a cicatricial tissue is formed. Thus, a mean is necessary, such as covering surroundings of collagen with a material which prevents migration of fibroblast.
On the other hand, it is known that certain ceramics (for example, as bioactive glass, Bioglass (registered trademark), crystallized glass A-W (Cerabone (registered trademark) A-W)) bond with a bone in a living body. This bonding between ceramics and the bone is attributed to formation of a hydroxy-apatite layer on a surface of ceramics in a living body (or in an aqueous solution having an ion concentration close to that of a human body fluid). A bonding mechanism is considered that a silicate ion or a silanol group formed on a surface of the ceramics is first reacted with calcium and phosphoric acid ions in a living body or an aqueous solution to form a core of hydroxy-apatite, and the core grows by incorporation of supersaturated calcium and phosphoric acid ions in the living body or the aqueous solution on the basis of the core.
Patent Document 8 proposes a method for coating a bioactive layer by coating a liquid silica hydrosol or hydrogel on a base such as a metal and ceramics having various shapes such as plate-like, rod-like, fibrous and granular shapes, drying and heating it to bond the silica gel to the base, and immersing the base in an aqueous solution containing calcium and phosphoric acid ions at amounts supersaturated against hydroxy-apatite (mimetic body fluid), thereby, coating a hydroxy-apatite layer on a surface of the base. This document describes that an apatite-coated material can be applied to an artificial bone, and a bio-implantable medical material, device or equipment, etc. However, such the inorganic biomaterial has insufficient biocompatibility such as cell adhesion.
Moreover, an organic-inorganic complex material as a biomaterial is also investigated. For example, Patent Document 12 discloses an organic-inorganic complex biomaterial constituted of hydroxy-apatite of an average fiber length not less than 60 μm and collagen (collagen or a collagenous protein from mammals, birds, fishes, and genetically-engineered collagen, etc.). In addition, this document also describes that the aforementioned complex material can be produced by maintaining a concentration of calcium and phosphoric acid ions in a reaction vessel at a particular level such as by controlling a concentration of a starting material or a flow rate, and pressure-forming the complex prepared. In addition, Non-Patent Document 5 describes a method for complexing collagen and hydroxy-apatite by neutralizing acid-solubilized collagen derived from rat tail tendon in the presence of 0.1 M of CaCl2 and 0.1 M of NaH2PO4.
However, even in such the complex, there is a risk of pathogen (or pathogenic factor) infection (or propagation) when natural collagen is used as collagen.
In addition, Patent Document 13 discloses a method for producing a complex by contacting an aqueous solution containing calcium and phosphoric acid ions with a base containing sericin to deposit apatite on the base.
In addition, Patent Document 14 discloses a medical treating material in which a particular peptide is immobilized on a base. The medical treating material has the high physiological activity, particularly has strong cell growth promoting action and/or cell adhesion action, and there is described that it is useful as a material or an agent for healing, adhering, reinforcing and/or regenerating a biological tissue.
In addition, Patent Document 15 discloses a peptide having osteogenesis promoting action and an osteogenesis promoting agent containing the peptide as an active agent, which are useful for treatment of fractures, suppression of osteopenia in osteoporosis and a periodontal disease, and prevention of fractures in osteoporosis or rheumatic arthritis.
In addition, Non-Patent Document 6 describes that osteoid calcification is induced over 7 weeks by implanting into a rat crural muscle a material which is prepared by conjugating a peptide having osteogenic action, Lys-Ile-Pro-Lys-Ala-Ser-Ser-Val-Pro-Thr-Glu-Leu-Ser-Ala-Ile-Ser-Thr-Leu-Tyr-Leu-NH2 (SEQ ID NO: 2) to an alginate gel crosslinked with ethylenediamine.
In addition, Non-Patent Document 7 describes that differentiation of a neural stem cell derived from rat hippocampus into a nerve cell is markedly promoted by culturing the neural stem cell on a material prepared by conjugating a peptide having differentiation promotion action for neural stem cells, Tyr-Arg-His-Ala-Trp-Ser-Glu-Asn-Leu-Ala-Gln-Cys-Phe-Asn-NH2 (SEQ ID NO: 1) to the alginate gel.
[Patent Document 1] JP-A 08-027192
[Patent Document 2] JP-A 07-097454
[Patent Document 3] JP-A 08-053548
[Patent Document 4] JP-A 07-278312
[Patent Document 5] JP-A 05-000158
[Patent Document 6] JP-A 05-125100
[Patent Document 7] JP-A 06-228506
[Patent Document 8] JP-A 08-276003
[Patent Document 9] JP-A 08-041425
[Patent Document 10] JP-A 2003-321500
[Patent Document 11] JP-A 5-103829
[Patent Document 12] JP-A 2003-190271
[Patent Document 13] JP-A 2003-154001
[Patent Document 14] JP-A 2006-272002
[Patent Document 15] JP-A 2003-73400
[Non-Patent Document 1] Methods Enzymol., Vol. 82, pp. 33-64 (1982)
[Non-Patent Document 2] J. Mol. Biol., Vol. 63, pp. 85-99 (1972)
[Non-Patent Document 3] Int. J. Peptide Protein Res., Vol. 46, pp. 453-463 (1995)
[Non-Patent Document 4] Nature Review, Vol. 2, pp. 118-126 (2001)
[Non-Patent Document 5] Chem. Mater., Vol. 15, pp. 3221-3226 (2003)
[Non-Patent Document 6] J. Biomed. Master Res., Vol. 70A, pp. 115-121 (2004)
[Non-Patent Document 7] Cell Transplant, Vol. 14, pp. 665-672 (2005)